A component built-in wiring substrate includes a first insulating layer, a first conductor layer formed on a first surface of the first insulating layer and including a component mounting pad, a second conductor layer formed on a second surface of the first insulating layer on the opposite side with respect to the first surface, via conductors formed in the first insulating layer such that the via conductors are connecting the second conductor layer and the component mounting pad of the first conductor layer, a second insulating layer formed on the first insulating layer and having a component accommodating portion penetrating through the second insulating layer such that the component mounting pad is positioned at bottom of the accommodating portion, and an electronic component positioned in the accommodating portion of the second insulating layer such that the electronic component is mounted on the component mounting pad of the first conductor layer.